Randy, here's a legal question for you. Assume for a moment that this proposal was to get enacted. What would be the British government's liability if criminals were to exploit a vulnerability while Apple is waiting for permission to release a security update?
Well, first, understand that I am an attorney licensed in California in the U.S. I'm not any sort of expert on British law.
That said, British law and U.S. law are extremely similar in some ways, one having been based on the other. I'd assume that there would be two laws in Britain similar to ones in the U.S.
The first says that you can't sue the government for things that they do in the ordinary course of business. So, you can't sue the government for enacting laws that you don't like, or which you suffer personal harm from, assuming that the laws are enacted properly in the ordinary course of government doing what it is supposed to do. So, if the President of the U.S. enacts a tariff on imports, and that leads to a trade war and your, lets says soybeans, suddenly have no market, and you lose everything, you aren't entitled to sue the government.
Second, to sue for harm due to negligence, you have to show that the negligent act could have been directly foreseen to have caused harm to a particular defendant. Not a class of potential defendants, but a particular one. Otherwise, the act is deemed to be too attenuated from the harm caused to rise to the level of negligence. The common law school example is the government closes two lanes of a three lane bridge. You are late to work because of the traffic backup. You can't sue for your damages because the act in question couldn't be specifically forseen as effecting you personally.
So, to answer your question directly, if criminals were to break into your iPhone, because of the proposed law, and steal a bunch of stuff that harms you, you are probably SOL.